1. Field of the Invention
The invention relates to phase comparing method and apparatus, more particularly to phase comparing method and apparatus in which a sampled periodic signal has a predetermined resolution.
2. Description of the Related Art
Phase comparison between two periodic signals is commonly applied to a phase-locked loop, and a servo loop in an optical recording apparatus, such as CD-ROM, DVD-ROM, DVD-RAM. At present, a digital signal processor (hereinafter referred to as DSP) is used to conduct phase comparison between two periodic signals. An allowable sampling signal frequency for a DSP depends on a sampling frequency of the DSP and a signal resolution, i.e., the allowable sampling signal frequency=the DSP sampling frequency/the signal resolution. For example, if the sampling frequency is 1 kHz, the allowable sampling signal frequency is 100 Hz when a sample signal obtained by sampling the periodic signal has 10 sampling points. Therefore, when the DSP sampling frequency is fixed, the higher the frequency of the periodic signal frequency, the lower will be the signal resolution of the sample signal, which can result in error during phase comparison.